Limitations in Thermal Degradation Modelling and Kinetic Parameters Evaluation for Polymeric Blends in Dynamic ThermogravimetryPresented by:Dr. Abdul Rehman Khan – Consultant Environment & Life Sciences Research Center Kuwait Institute for Scientific Research5th Technology Innovations Conference& Exposition.2nd November 2014, Kuwait

1. Introductory Remark.

2. Motivation of Work and Benefits to Clean Fuels.

3. Used Models in Literature.

4. Case Study: Degradation of PET/PMMA & Integral Method

Development.

5. Conclusions & Future Work

Presentation Agenda

Introductory Remark

• Thermal degradation of polymers is arguably one of the

hottest topics in engineering disciplines.

• Typically, results are conflicted especially in micro-scale and

in particular, dynamic thermogravimetric analysis (TGA).

• Such discrepancies result from different factors, such as:

– Experimental setups: Different inert atmospheres (at different scales),

temperature ranges, sample amounts, heating rates (b) and

pressures.

– Adequacy of the kinetic model: Modelling approach and assumptions.

– Thermal lag (T): Heat transfers problems.

• Waste is accumulating in Kuwait with NO GOVRMT

scheme to handle.

• Plastic solid waste (PSW) is estimated at 200 Mtpa.

(2013).

• PSW is typically shipped abroad (exported)/recycled in

private company(ies) for profit.

• THIS IS A WASTE!!!

• Being a crude oil product, plastics encompass energy

that should be taken advantage of.

Introductory Remark

Item CV (MJ kg-1) Item CV (MJ kg-1)PE

PP

PS

Kerosene

43.3-46.5

46.50

41.90

46.50

Gas Oil

Heavy Oil

Petroleum

Household PSW mixture

45.20

42.50

42.30

31.80

Table 1: Calorific Value of Major Polymers in Comparison toCommon Fuels.

Pyrolysis Hydrogenation Gasification

Kiener N

oell

BASF

BP

ABB

VKE

Texaco

Eisenmann W

inkler

Lurgi

SVZ

VEBA -Oel

Oil OilNaphtha &High Boiling Oil

Thermolysis

Main advantages include:

1. Minimal pre-treatment.

2. PCs production & Integration.

3. Waste disposal solution.

4. Sustainable energy source.

Motivation• Today’s refining capacity of Kuwait is around 936 mbpd divided.

• Post CFP, the refining capacity of the country will decrease to a total of

800 mbpd.

• It is anticipated that the NRP will process 615 mbpd of Kuwait Export

Crude (KEC, API≈30). Total refining capacity will be: 1,415 mbpd.

Table 2: Major products specs post CFP (Sulfur ppm).

Product Current Spec. Post CFP

Full Range Naphtha

Gasoline (All Grades)

Gas Oil 1 (Including Domestic Use)

Gas Oil 2

Gas Oil 3 (New Grade)

Fuel Oil (%)

700

500

2000-5000

500

-

4.5

500

10

10-500

10

10

1

• Products from TCT units is the answer. Such include H2, C3, C4, etc. This will intensify production of chemical feedstock from a renewable energy source.

• Polymers, in the form of plastics, are fed to pyrolysis

reactors as a fraction of MSW. They are a mixture of

polymers, not just a single one. Hence, predicting their

degradation behavior and evaluating their kinetic

parameters in a blend is a must.

Problem Statement

Most common kinetic degradation models are isoconversionones:

1. Ozawa-Flynn-Wall:• One of the most used expressions in literature.• This method is considered to be the most exact.• Assumes a first order kinetics (n=1).

2. Friedman’s method:

Established Models

RTE

mmRAE a

oa 05.1)1(33.5)/ln()ln(

RTEmmfAdtdm

m oo

/)(ln)ln()/)(1ln(

• Blends of PET/PMMA (traded under the name of Ropet) are typically used in

electrical applications.

• Hence studying their thermal degradation and stability determines optimal

operating condition of these blends avoiding electrical overshoots in

electronics.

• Thermogravimetric analysis (TGA) was carried out for the blends with pure

dry nitrogen purge of 20 cm3/min.

• Four were used: 5, 10, 15 and 20oC/min.

PET/PMMA Degradation as a blend

Mathematical DerivationThe expression of degradation could be written after rearranging the denominatoras:

dtkxdx

np

P

The results presented in this work reflect first order kinetics. Integrating the resultingexpressions results in the following for each polymer in the blend:

t

B

x

pB

pB

t

A

x

pA

pA

dtkxdx

dtkxdx

pB

pA

01

01

For a given blend of known composition (xA is the PET fraction in the blend), theoverall cumulative weight loss expression will be given as

teAxteAxx RTEA

RTEAp

aa )/(2

)/(1

21 exp)1(exp

N

1i (exp)p

(th)p(exp)P

x

xxmin(O.F.)FunctionObjective

• Several non-isothermal pyrolitic degradation TG curves have been modelled

in this study.

• It was noticed that with the increase of PET fraction in the blends, the TG

curve showed a shift to higher value in the degradation temperature till 75

wt%.

• The 90/10 (wt/wt%) blend of PET/PMMA started decomposing at almost 600

K (beginning of the first shoulder incline).

• Virgin PET and PMMA typically started decomposing at temperatures

around 630 K and 560 K, respectively.

Results & Observations

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

500 550 600 650 700 750 800

PET/PM

MA (50/50

 wt/wt%

)

Temperature (K)

Exp.Theor.

Model vs. experimental results for PET/PMMA blend

(25/75 wt/wt%) at 5= oC/min.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

500 600 700 800 900

PET/PM

MA (50/50

 wt/wt%

)

Temperature (K)

Exp.Theor.

Model vs. experimental results for PET/PMMA

blend (50/50 wt/wt%) at 10= oC/min.

• The structural and physical properties of blends of both polymers affect the TG

curves, where the abundance of PET in the 90/10 blend delays the degradation to a

point where the material acts almost like a virgin PET (or pseudo virgin material).

PET/PMMA (25/75) (wt/wt%) PET/PMMA (50/50) (wt/wt%)Ea1 (kJ/mol) Ea2 (kJ/mol) A1 (min-1) A2 (min-1) r2 Ea1 (kJ/mol) Ea2 (kJ/mol) A1 (min-1) A2 (min-1) r2

= 5 oC/min

= 10 oC/min

= 15 oC/min

= 20 oC/min

240

230

220

210

140

130

120

110

1.1x1019

1.03x1017

3.2x1018

5.5x018

1.73x109

2x1011

2.7x108

1.33x104

0.98

0.98

0.98

0.98

250

240

230

220

150

140

130

120

3.9x1015

1.82x1016

2.2x1017

4.2x017

2.7x1010

8.1x1010

2.28x107

2.7x1011

0.99

0.99

0.97

0.99

PET/PMMA (75/25) (wt/wt%) PET/PMMA (90/10) (wt/wt%)

Ea1 (kJ/mole) Ea2 (kJ/mole) A1 (min-1) A2 (min-1) r2 Ea1 (kJ/mol) Ea2 (kJ/mol) A1 (min-1) A2 (min-1) r2

= 5 oC/min

= 10 oC/min

= 15 oC/min

= 20 oC/min

260

250

240

230

160

150

140

130

3.12x1014

2.89x1015

7.6x1016

1.27x017

6.23x108

2.92x109

6.62x107

4.28x106

0.99

0.99

0.98

0.99

270

260

250

240

170

150

150

140

2.32x1016

2.7x1016

6.23x1015

1.4x016

6.4x107

5.9x107

2.1x109

1.07x1010

0.99

0.99

0.98

0.99

Apparent activation energy evaluated for PET (Ea1) and PMMA (Ea2), pre-

exponential factors (A1 and A2) and regression coefficient between experimental

and theoretical fits.

• A general mathematical expression based on the integral solution of

different PET/PMMA blends for non-isothermal (dynamic)

thermogravimtry (TG) has been developed.

• The model results show good agreement with experimental values

depicting the true pyrolitic reaction mechanism.

• The apparent discrepancies are attributable to melt mixing resulting

in the formation of different phases.

• Thermal lag was caused by the evaporation of volatile degraded

products (heat absorption) and also greatly influenced by thermal

characteristics of blend of polymers ensuing in the observable

deviation among experimental and model results.

Conclusions

Thank you

Dr. Abdul R. Khan (Consultant-ELSRC)

Dr. Sultan Al-Salem (PRC)